The present disclosure generally relates to a flexible manufacturing system and, more particularly, to a reconfigurable fixture device for clamping and/or providing support for a variety of different workpiece configurations.
The advent of assembly lines has enabled rapid, mass production of products at a reduced product cost. Assembly lines typically include multiple operation stages and component, material, or sub-assembly inputs. Sometimes the workpieces are similar or related part shapes. Other times, the workpieces are of unrelated design but require similar manufacturing operations. In these varied applications, the fixture reconfiguration or changeover from one part design to another has to be fast enough to meet the productivity requirements of current manufacturing systems.
Previous efforts in designing and developing flexible fixturing for either small batch manufacture or mass production scenarios can generally include the use of modular fixtures and conformable fixtures. Modular fixturing generally includes fixtures assembled from a standard library of elements such as V-blocks, toggle clamps, locating blocks, and the like. Their flexibility lies in the ability to be reconfigured either manually or by a robotic device. However, modular fixtures have no intrinsic ability to adapt to different sizes and shapes of parts within a part family. In addition, the time necessary for reconfiguration is long. As a result, modular fixtures are more suited to a job shop environment than mass production.
The advent of Flexible Manufacturing Systems (FMS) in the early 1960's provided the impetus for work on conformable fixturing. A conformable fixture is defined as one that can be configured to accept parts of varying shape and size. Conformable fixture technology generally includes encapsulant or mechanistic techniques. Examples of encapsulant fixtures are found in the aerospace industry, where low melting-point metals are used to enclose turbine blades and produce well-defined surfaces for part location and clamping for grinding operations. While an excellent means of facilitating the holding of complex parts, encapsulation is a costly and time-consuming process.
Mechanistic fixtures reported in the literature include the use of petal collets, programmable conformable clamps, a programmable/multi-leaf vise, and an adjustable integral fixture pallet. Of the four, the adjustable integral fixture pallet concept appears to be the most capable of accommodating a part family of castings. To date, however no feasibility studies have been conducted regarding the applicability of any of these techniques to production machining operations.
One troublesome area in flexible manufacturing systems is its implementation in body shops. Clamps are typically employed to clamp the various sheet metal workpieces (e.g., body panels) during assembly and clamping can potentially scratch the exposed surface and/or locally deform the workpiece or surface coating, affecting its aesthetic quality. While, ideally, clamping could be performed on flanges or surfaces that are invisible or immaterial to end users, some clamping inevitably occurs on surfaces whose quality is important aesthetically.
Current clamps utilized in assembly lines generally include a metal (e.g., tool steel) clamp block, which accurately matches the contours of the workpiece and a matching pressure foot. In operation, the clamp block with a contoured surface supports the exterior surface of the workpiece while the pressure foot contacts the inner (non-exposed) surface. As a result, the contour of each clamp block is generally specific to a limited number of workpieces. In dedicated facilities, the contours of the clamp block are generally fabricated by numerically controlled (NC) machining using data generated from the workpiece to be fixtured. A problem arises if multiple models having significantly different workpiece configurations are to be produced on the same tooling setup. Multiple clamp blocks having different contours are then required to accommodate the multiplicity of workpiece configurations.
Clamps with a compliant pad and a matching pressure foot are also used in assembly lines for fixturing workpieces with aesthetically important surfaces. In operation, the clamp block with a contoured surface supports the exterior surface of the workpiece while the pressure foot contacts the inner (non-exposed) surface. The compliance of the clamp block ensures that the surface is not marked and the rigidity of the pressure foot ensures that the location of the part is known completely (to within the tolerance imposed by the deformation of the part under the clamp loads), i.e., the part is not floating with regard to the clamp block. With this approach, minor differences between the shape of the workpiece and the clamp block geometry can be accommodated without introducing local deformation. As a result, the contour of each clamp block is generally specific to a limited number of workpieces. In dedicated facilities, the contours of the clamp block are generally fabricated by numerically controlled (NC) machining using data generated from the workpiece to be fixtured. A problem arises if multiple models are produced having significantly different workpiece configurations. Multiple clamp blocks having different contours are then required to accommodate the multiplicity of workpiece configurations.
Accordingly, there remains a need for a reconfigurable fixture device that can provide adequate support and/or clamping means for a variety of workpiece configurations.